KB6NU's Ham Radio Blog

KB6NU's Ham Radio Blog

Test Equipment

LC Meter, Revisited

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A lot of hams swear by the AADE LC Meter. It seems like a relatively accurate instrument, and the price is right—$100 for a kit, $130 for an assembled unit.

Today, however, I just received a press release from Agilent (the company that used to be Hewlett Packard), touting two new LCR meters – the U1731A and U1732A. These look like really nice instruments that hams will want to take a look at.

The U1731A sells for $275, while the U1732A sells for $330. As far as I can tell from the spec sheet, the only difference between the two is that the U1731A has two test frequencies—120Hz and 1 kHz—while the U1732A has four test frequencies—100 Hz, 120Hz, 1 kHz, and 10 kHz.

As you might expect with a professional instrument, there’s a three-year warranty on the instrument. There are also a number of useful options for the U1731A/U1732A, including a carrying case ($20), SMD tweezer ($30), and AC power adapter ($35).

Looks like a great instrument to me. It would be interesting to get one and compare it head-to-head with the AADE meter.

More than just an antenna analyzer

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On the Elecraft mailing list, there’s been a flurry of messages recently about LCR meters. One of the units touted was a unit from a company called Almost All Digital Electronics. They have both a kit version ($100) and an assembled version ($130). A couple of the guys even bought and built it.

I chimed in with the opinion that instead of buying yet another meter, that they should just buy an antenna analyzer to make those measurements. My analyzer can measure inductance and capacitance directly, and do so at any frequency up to 35 MHz. It may not be quite as accurate as the LCR meter, but my guess is that it’s plenty accurate for amateur use. And to top it off, I get to use it to analyze my antennas!

One of the non-conventional ways that I use the antenna analyzer is to demonstate the principles of reactance and impedance to my General class students. First, I measure the reactance of a coil that I’ve had around the shack for ages (at one time, I used it as a loading coil coil for a vertical antenna). I show how the reactance increases with frequency, then record the reactance at 6 MHz.

Next, I measure the resistance of a 150-ohm precision resistor that came with my analyzer. Then, I calculate the impedance with the equation Z = sqrt(XL**2 + R**2).

I then connect the resistor in series with the coil and measured the impedance. Surprisingly (or, not so surprising, actually) the measured impedance is almost exactly what I calculate.

Actually, my analzyer–the Autek VA1–is not an antenna analyzer at all. It’s called a vector analyzer. Most of the high-end antenna analyzers can make these kinds of measurements. They can also be used as low-level RF signal generators. So, while they’re most useful at analyzing antenna parameters, they can be used for more than just that.

 

How to use an oscilloscope

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updated 3/15/12

On the Elecraft mailling list, there was a request for help finding an oscilloscope tutorial. Since this is right up my alley–I’ve written for Test&Measurement World magazine for a zillion years–I thought I’d do a little research.

A Google search turned up a bunch of online tutorials. When I first posted this in 2004, one of the tutorials that I liked was http://www.oscilloscope-tutorials.com. Unfortunately that website is no longer online. Instead, go to YouTube, and have a look at How to use an oscilloscope, a video produced by two young Tektronix engineers that explains the basics of a scope’s vertical and horizontal controls and triggering.

Another tutorial that I liked is an article from the American QRP Club website. Written by Paul Harden, NA5N, this long article explains not only how scopes work, but also how to check and calibrate a scope that you may have purchased at a hamfest. Very useful info.